College Algebra
posted by Anonymous on .
You have 800 feet of fencing to enclose a rectangular plot that borders on a river. If you do not fence the side along the river,find the length and width of the plot that will maximize the area. What is the largest area that can be enclosed?

I know how to do this with calculus, but algebraically it starts the same way.
L + 2W = 800 L = 800  2w
A = LW
A= (8002w)w
A = 800w  2w^2
Take the derivative: 800 4w
800 4w = 0 to find max.
800 = 4w
200 =w
l = 400 
Thank you!

How did it become 8004w from 24002w^2?